Drainage pipe has long been used for transporting water in various agricultural, residential, civil engineering, and other construction applications. For example, drainage pipe has been used to create storm sewer systems configured to collect and dispose of water “run-off.” Traditionally, drainage pipe was made from clay or concrete, which caused the pipe to be heavy, expensive, and brittle. In order to improve the ease-of-installation, cost-effectiveness, and durability of drainage pipes, pipes are now often manufactured from alternative materials, including various polymers and polymer blends.
One method of manufacturing polymer pipe involves forming a polymer pipe and then extruding an outer layer of polymer onto the outside of the polymer pipe. As a result, the outer layer of polymer constitutes an outer pipe wall that is fused to the exterior surface of the polymer pipe. This outer layer of polymer is generally extruded at a temperature sufficiently high to allow it to bond with the exterior surface of the polymer pipe. Specifically, the extruded outer layer of polymer is extruded at a temperature hot enough to at least partially melt the exterior surface of the polymer pipe, such that polymer chains of the exterior surface and the extruded outer wall intersperse and then cool together. This results in the exterior surface and the extruded outer wall being integrally fused or bonded together wherever they contact each other.
Even when the outer layer of polymer is extruded at a high temperature, the outer layer can sometimes insufficiently bond or fuse to the exterior surface of the pipe. Specifically, even though a very thin layer of the exterior surface may weld to the newly extruded outer layer, the level of bonding may be too shallow to provide a sufficient weld between the outer layer and the exterior pipe surface. Thus, a high extrusion temperature can sometimes be insufficient for thoroughly bonding an outer layer beyond the immediately exterior surface of a polymer pipe.
Accordingly, there is a need for an apparatus and method for pressing an outer wall of pipe to achieve sufficient bonding between an outer layer of polymer and the polymer pipe.